In a typical mixer-settler, in the first step, the aqueous and organic phases are pumped into a mixer or mixers in order to achieve a uniform liquid-liquid dispersion and a small droplet size. In The VSF® technology (stands for Vertical Smooth Flow) developed by the applicant this first step is performed in a pumpmixer called Dispersion Overflow Pump (DOP®) (disclosed e.g. in document U.S. Pat. No. 5,662,871) and in a set of two SPIROK® helical mixers (disclosed in e.g. document U.S. Pat. No. 5,185,081). After mixing, the dispersion is fed into a settler. The settler is typically a large tank which is square in plan and its square area is about several hundred square meters. Dispersion is fed into the settler at the front end of the settler. A distributor fence is arranged at the feed end of the settler to distribute the flow of the dispersion to the whole width of the settler. In the settler, the dispersion moves towards the settler back wall and, at the same time, the phases separate by gravity into two layers with a dispersion band remaining between them. Typically, separation fences are arranged in the settler tank to enhance coalescence of the dispersion. In the VSF® technology the separation fences are so-called DDG® fences (Dispersion Depletor Gate) (disclosed e.g. in document U.S. Pat. No. 7,517,461). At the rear end of the settler, an adjustable weir and launders are used to control the vertical position of the phase interface and to collect and discharge both phases, respectively. Arrangements of launders are disclosed e.g. in documents WO 97/40901, WO 2009/063128 A1 and WO 2010/097516 A1.
The settler tank is normally built on the site. WO 2007/135221 A1 discloses one method for manufacturing a mixer-settler on site. Wall structures are connected by vertical support columns to the bottom plate. The wall structure is formed by fastening a required number of horizontal support beams to the vertical support columns at regular intervals. A required number of plate-like wall elements made of a chemically resistant material are attached to the horizontal support beams inside the mixer-settler, so that they form a load-bearing structure in the spaces left between the horizontal support beams. The plate-like wall elements are connected to the plate-like element covering the bottom plate of the mixer-settler. However, as mentioned, such a settler is still a large tank which is square in plan and its square area is about several hundred square meters.
So far, a solvent extraction plant has been project specified. In each case the layout of the plant and the equipment have been unique. There has not been a possibility for the productization of settlers. Settlers known in the prior art require most of the construction work to be done at site. This causes problems because of the crucial influence of local factors. It has been difficult to control the quality of the site work by local suppliers. Conventional settlers are normally permanent structures. At the end of their often relatively short life cycle it is not possible to recycle the settler by dismantling it and then building it up again to be used at another site. WO 2009/004321 A1 discloses a small-scale settler tank being dimensioned to be sufficiently small that it may be transported by a conventional truck and trailer without a need for specialist transport vehicles. This is enabled by dimensioning the complete settler tanks such that they are not larger than a shipping container. The settler tank may be dimensioned so that it fits inside a shipping container. However, the problem is that the settler tank itself does not provide standard shipping container characteristics, such as a self-supporting structure to provide handling and stacking capability.